SixXS::Sunset 2017-06-06

Neighbor Unreachability Detection in 6in4 Tunnels
[se] Carmen Sandiego on Tuesday, 23 October 2012 18:24:56
Hello, I'm working with implementing 6in4 tunnel according to RFC 4213. What puzzles me is section 3.8 Neighbor Discovery over Tunnels. How are Neighbor Unreachability Detection probes sent and replied to? Shall a tunnel endpoint encapsulate IPv6 neighbor discovery packets to resolve the other node's inner IPv6 address? This is odd since there is no link-layer address to resolve since the packets are tunneled in IPv4. What is the reply? Thanks in advance. David
Neighbor Unreachability Detection in 6in4 Tunnels
[ch] Jeroen Massar SixXS Staff on Tuesday, 23 October 2012 19:48:21
There is a link-local address. Every single interface that is IPv6 enabled has to have one. For AYIYA we use a good portion of the IPv6 address on that link to generate a link-local address. Other implementations use the IPv4 address etc.
Neighbor Unreachability Detection in 6in4 Tunnels
[se] Carmen Sandiego on Thursday, 25 October 2012 14:25:53
Thanks for your quick reply. I managed to get NUD enabled in my tunnel and had a chance to get a look at the packets so now I understand. My mistake were that I though it would not be possible to send a Neighbor Advertisements in response to a solicitation since there would not be any link layer (MAC) address associated with the inner IP of the tunnel. I realized that it is possible to send "empty" Neighbor Advertisments, as response to a Neighbor Solicitations. These advertisements do no contain any information about the link layer address (MAC address) - perfect for a tunnel encapsulated packet.

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